Is it an issue need to be resolved? += (("a", 1))

[dongxuwang]

For += with tuple, why I have to add () to wrap the tuple value

import collection.mutable.ArrayBuffer
val x: ArrayBuffer[(String, Int)] = ArrayBuffer(("a", 1))
// x += ("b", 2) // this wouldn't work
x += (("b", 2))

[EugeneFlesselle]

Apparently, we untuple tuple arguments of infix operations if the function does not consist only of unary alternatives.

trait Buffer1[A]:
  def += (elem: A): Buffer1[A]

val b1: Buffer1[(String, Int)] = ???
b1 += ("a", 1) // Ok


trait Buffer2[A]:
  def += (elem: A): Buffer2[A]
  def += (elem1: A, elem2: A): Buffer2[A]

val b2: Buffer2[(String, Int)] = ???
b2 += ("b", 2) // Error

scala3/compiler/src/dotty/tools/dotc/typer/Applications.scala

Lines 1231 to 1239 in 6bb6b43

	/** Should we tuple or untuple the argument before application?
	* If auto-tupling is enabled then
	*
	* - we tuple n-ary arguments where n > 0 if the function consists
	* only of unary alternatives
	* - we untuple tuple arguments of infix operations if the function
	* does not consist only of unary alternatives.
	*/
	def needsTupledDual(funType: Type, pt: FunProto)(using Context): Boolean =

[som-snytt]

Since the alternative Growable#+= is deprecated, it would be handy if it were ignored for purposes of infix untupling. Hopefully it can be removed someday.

The current nice syntax is x += "b" -> 2.